Amplifiers can be generally classified as operational amplifiers or limiting amplifiers. An operational amplifier receives an input signal and generates a signal that has an amplitude different from the amplitude of the input signal. The frequency components of the generated signal are substantially identical to the frequency components of the input signal.
In contrast, a limiting amplifier receives an input signal and generates a signal having a specified peak-to-peak amplitude. The specified amplitude is identical for any input signal that is within the operating range of the limiting amplifier. In a limiting amplifier, the frequency components of the output signal may differ from the frequency components of the input signal.
Some applications require an amplifier to provide a particular gain over, a particular bandwidth. In the case of a limiting amplifier, the particular gain may be represented by a minimum input signal that must be amplified to a specific peak-to-peak amplitude over the particular bandwidth. A conventional limiting amplifier is unable to suitably satisfy these requirements for some existing applications. One such application is described in the OC-192 10Gb/s optical signaling specification.
Conventional limiting amplifiers may present other drawbacks. A conventional limiting amplifier consumes significant die space when fabricated as an integrated circuit. Moreover, the gain provided by some existing limiting amplifiers varies unacceptably with process.